Fine tuning of emission spectra by combination of multiple emitter spectra

ABSTRACT

A first device is provided. The first device includes an anode, a cathode and an emissive layer disposed between the anode and the cathode. The emissive layer includes a first organic emitting material having a first peak wavelength and a second organic emitting material having a second peak wavelength. The emissive layer has a homogenous composition. The second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.

The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices having desired emission characteristics, and methods of fabricating such devices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

As used herein, and as would be generally understood by one of skill in the art, the term “emitting” as used to describe a material in a device refers to a material that emits a significant amount of light when the device is operated under normal conditions. For example, Ir(ppy)₃ is a well known emissive organic material. Ir(ppy)₃ may be used as an emitting material in an OLED, generally by including it in the emissive layer with a host, in a device designed such that recombination occurs in or near the layer containing Ir(ppy)₃, and such that emission from the Ir(ppy)₃ is energetically favored. However, Ir(ppy)₃ may also be used in an OLED as a material that is not an “emitting” material. For example, it is known to use Ir(ppy)₃ as a hole transport material in a hole transport layer, such that the Ir(ppy)₃ functions to transport holes to an emissive layer where a different material emits light. In this context, Ir(ppy)₃ is not considered an “emitting” material.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

A first device is provided. The first device includes an anode, a cathode and an emissive layer disposed between the anode and the cathode. The emissive layer includes a first organic emitting material having a first peak wavelength and a second organic emitting material having a second peak wavelength. The emissive layer has a homogenous composition. The second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.

In one embodiment, the first and second organic emitting materials are phosphorescent organic light emitting materials.

Preferably, the second peak wavelength is between 12 and 28 nm greater than the first peak wavelength.

In some embodiments, first device of claim 1, the first device emits a third peak wavelength that is between the first peak wavelength and the second peak wavelength. Preferably, the concentration of the first organic emitting material in the emissive layer is C1, the concentration of the second organic emitting material in the emissive layer is C2, the first, second and third peak wavelengths are λ1, λ2, and λ3, respectively, and the third peak wavelength λ3 is within 4% of:

((λ1C1)+(λ2C2))/(C1+C2).

In some embodiments, wherein the FWHM of the emissive spectrum of the first device is less than the greater of the FWHM of the emissive spectrum of (i) a second device that is the same as the first device in all respects except that it includes the first emitting material but not the second emitting material, and (ii) a third device that is the same as the first device in all respects except that it includes the second emitting material but not the first emitting material.

In some embodiments, the measured FWHM of the emissive spectrum of the first device is less than the combined emission of the first and second emitting materials calculated based on the proportions of the first and second emitting materials present in the emissive layer. In some embodiments, the measured FWHM of the emissive spectrum of the first device is at least 10% less than the combined emission of the first and second emitting materials calculated based on the proportions of the first and second emitting materials present in the emissive layer.

In some embodiments, the first device is an organic light emitting device.

In some embodiments, the first device is a panel that includes a plurality of organic light emitting devices controlled by an active matrix.

In some embodiments, the first device is a consumer product.

A method of fabricating a first device is provided. A first container is provided that contains, in a desired proportion: a first organic emitting material having a first peak wavelength, and a second organic emitting material having a second peak wavelength. A substrate is provided having a first electrode disposed thereon. An emissive layer is deposited over the first electrode, wherein the first container is a source of material for depositing, and wherein the emissive layer comprises the first and second organic emitting materials in the desired proportion. A second electrode over the first emissive layer. The second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.

In some embodiments, depositing the emissive layer further comprises depositing an organic host along with the first and second organic emitting materials. The organic host may be included in and deposited from the first container, and/or may be deposited from a second container.

Embodiments and preferences discussed above with respect to devices are also applicable to methods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows a schematic structure of devices that were fabricated having variable [%] of emitters C and D, used with Example 1.

FIG. 4 shows electroluminescent (EL) spectra of the devices of Example 1.

FIG. 5 shows maximum wavelength and full width half maximum (FWHM) values for the devices of Example 1. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 6 shows the FWHM difference (experimental vs. calculated) values for the devices of Example 1.

FIG. 7 shows schematic structure for the devices of Example 2 with variable [%] of emitters A and B.

FIG. 8 shows EL spectra of the devices of Example 2 with variable [%] of emitters A and B.

FIG. 9 shows maximum wavelength and FWHM values for the devices in Example 2 with variable [%] of emitters A and B. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 10 shows a schematic structure for the devices in Example 3 with variable [%] of emitters B and C.

FIG. 11 shows EL spectra for the devices of Example 3 with variable [%] of emitters B and C.

FIG. 12 shows maximum wavelength and FWHM values for the devices of Example 3 with variable [%] of emitters B and C. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 13 shows a schematic structure for the devices of Example 4 with variable [%] of emitters A and D.

FIG. 14 shows EL spectra for the devices of Example 4 with variable [%] of emitters A and D.

FIG. 15 shows maximum wavelength and FWHM values for the devices of Example 4 with variable [%] of emitters A and D. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 16 shows a schematic structure for the devices of Example 5 with variable [%] of emitters B and D.

FIG. 17 shows EL spectra for the devices of Example 5 with variable [%] of emitters B and D.

FIG. 18 shows maximum wavelength and FWHM values for the devices of Example 5 with variable [%] of emitters B and D. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 19 shows chemical structures for compounds used in device fabrication.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, and a cathode 160. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” LED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

A first device is provided. The first device includes an anode, a cathode and an emissive layer disposed between the anode and the cathode. The emissive layer includes a first organic emitting material having a first peak wavelength and a second organic emitting material having a second peak wavelength. The emissive layer has a homogenous composition. The second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.

The first device may include other emissive layers that do not necessarily meet the criteria described in the preceding paragraph. For example, the first device may include a first emissive layer that does meet the criteria of the preceding paragraph, such as inclusion of the first and second organic emitting materials as specified. The first device may further include a second organic emissive layer that does not meet the criteria, and that may, for example, have only a single emitting material, or a non-homogenous composition.

It is known to fabricate an OLED having multiple emitting materials, both in the same layer and in different layers. However, these OLEDs are generally directed to achieving broad spectrum emission. Thus, it is known, for example, to combine green and red emitting materials in a single layer. In this situation, triplets tend to transfer from the higher energy green emitters to the lower energy red emitters, such that proportion of emission from the lower energy red emitters relative to the green emitters may be significantly larger than the proportion of the concentration of red emitter to green emitter. To achieve balanced emission in this situation, those of skill in the art expect that the concentration of red emitter be much lower than the concentration of green emitter. The combined red-green emission may be further combined with blue emission from another layer in the same device, or blue emission from a different device, to achieve broad spectrum emission.

The purpose of embodiments disclosed herein is significant different. Embodiments disclosed herein are directed to using two different emitters in the same layer that emit similar spectra having similar peak wavelengths, with the goal of fine tuning the emission to a specific desired spectra. The desired spectra may be, for example, particular spectra of red, green and blue to which the human eye is particularly sensitive, and which may be required by certain manufacturing standards. By using fine tuning as disclosed herein, it is possible to use to emit a specific desired color two particularly good emitters in terms of lifetime, stability, efficiency, cost, ease of fabrication and the like. While each of the two particularly good emitters may not on their own emit the specific desired color, their emission may be combined as described herein to achieve the specific desired color.

In one embodiment, the first and second organic emitting materials are phosphorescent organic light emitting materials.

Preferably, the second peak wavelength is between 12 and 28 nm greater than the first peak wavelength.

The inventors have found, when combining two emitting materials in the same layer that have somewhat similar peak wavelengths as described here, that the peak wavelength is unexpectedly the concentration-weighted average peak wavelength of the two individual emitting material. This is contrary to conventional wisdom, which predicts that triplets will preferentially transfer to the lower energy material, such that the proportion of emission from the lower energy emitting material compared to the higher energy emitting material is expected to be more than the proportion of its concentration. Thus, in some embodiments, first device of claim 1, the first device emits a third peak wavelength that is between the first peak wavelength and the second peak wavelength. Preferably, the concentration of the first organic emitting material in the emissive layer is C1, the concentration of the second organic emitting material in the emissive layer is C2, the first, second and third peak wavelengths are λ1, λ2, and λ3, respectively, and the third peak wavelength λ3 is within 4% of:

((λ1C1)+(λ2C2))/(C1+C2).

In some embodiments, wherein the FWHM of the emissive spectrum of the first device is less than the greater of the FWHM of the emissive spectrum of: (i) a second device that is the same as the first device in all respects except that it includes the first emitting material but not the second emitting material, and (ii) a third device that is the same as the first device in all respects except that it includes the second emitting material but not the first emitting material.

“FWHM” or full width half maximum is a term known to the art that refers to the width of a peak at one half of the peak's maximum intensity. In the context of emissive spectra, FWHM is a measure of whether a spectrum is narrow or broad. Generally, narrow peaks have a smaller FWHM than broader peaks. A small FWHM corresponds to a narrow peak, which may also be referred to as more “saturated” than a broader peak. Saturated spectra are desirable in certain contexts, such as for use in displays that do not use color filters. Broad spectrum peaks are useful in other contexts, such as for use in displays that do use color filters, or to emit light for general illumination purposes with a high “CRI” (color rendering index).

The inventors have discovered that, when two emitters are combined in the same emissive layer as described herein, that the width of the total spectra is often less than expected from a calculation based on summing the contributions of the individual emitters. This result is observed in Examples 1, 3, 4 and 5. This result is unexpected. The “width” of a spectrum may be quantified using FWHM. Indeed, the inventors have observed many situations where the width of the total spectrum is even narrower, less than the width of one or preferably both of the spectra of the individual emitting materials that contribute to the total spectrum. This result is also unexpected. While not intending to be limited to any theory of why embodiments of the invention work, the inventors believe that the narrower than expected spectra are the result of the solvachromatic effect, as discussed, for example, in WO99-053724 Color-tunable organic light emitting devices. Forrest, Stephen R.; Bulovic, Vladimir; Thompson, Mark E.; Shoustikov, Andrei.

In some embodiments, the measured FWHM of the emissive spectrum of the first device is less than the combined emission of the first and second emitting materials calculated based on the proportions of the first and second emitting materials present in the emissive layer. In some embodiments, the measured FWHM of the emissive spectrum of the first device is at least 4% less than the combined emission of the first and second emitting materials calculated based on the proportions of the first and second emitting materials present in the emissive layer.

In some embodiments, the first device is an organic light emitting device.

In some embodiments, the first device is a panel that includes a plurality of organic light emitting devices controlled by an active matrix.

In some embodiments, the first device is a consumer product.

A method of fabricating a first device is provided. A first container is provided that contains, in a desired proportion: a first organic emitting material having a first peak wavelength, and a second organic emitting material having a second peak wavelength. A substrate is provided having a first electrode disposed thereon. An emissive layer is deposited over the first electrode, wherein the first container is a source of material for depositing, and wherein the emissive layer comprises the first and second organic emitting materials in the desired proportion. A second electrode over the first emissive layer. The second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.

In some embodiments, depositing the emissive layer further comprises depositing an organic host along with the first and second organic emitting materials. The organic host may be included in and deposited from the first container, and/or may be deposited from a second container.

Embodiments and preferences discussed above with respect to devices are also applicable to methods described herein.

The principle of fine emission tuning of the EL device spectrum is disclosed. As described herein, desirable emission spectrum can be obtained by combination of individual emitters spectra with certain ratio. If 2 emitters with λ1 and λ2 maximum wavelengths where λ1<λ2 are mixed in the device EML in certain ratio, then the maximum wavelength of the resulting device λ3 can be fine tuned within range from λ1 to λ2 by the tuning the relative concentrations of the emitters in the device EML and proportional to the emitters concentration.

The maximum wavelength λ3 of EL or PL emission of the device may be tuned to values between λ1 to λ2 max individual emitter wavelengths by the combination of individual emitters emission in the device, which can be achieved by placing of 2 corresponding emitters into the device EML in a desired concentration ratio. It has been shown that the maximum combined wavelength λ3 will be within λ1 and λ2 range and directly proportional to emitters concentration.

The combination of 2 emitter emission described herein may be useful for fine tuning device emission for a specific wavelength, e.g. to match a specific spectrum requirement for various applications. Such applications include OLED based flat panel displays and lighting.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but not limit to: a phthalocyanine or porphryin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and sliane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but not limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

k is an integer from 1 to 20; X¹ to X⁸ is CH or N; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit to the following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹—Y²) is a bindentate ligand, Y1 and Y² are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹—Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹—Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant.

Examples of metal complexes used as host are preferred to have the following general formula:

M is a metal; (Y³—Y⁴) is a bindentate ligand, Y³ and Y⁴ are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³—Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, triazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atome, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfanyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, host compound contains at least one of the following groups in the molecule:

R¹ to R⁷ is independently selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one aspect, compound used in HBL contains the same molecule used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

R¹ is selected from the group consisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

In another aspect, the metal complexes used in ETL contains, but not limit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 1 below. Table 1 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

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Two emitters are placed into a device EML and caused to emit simultaneously. λ1 is the maximum wavelength of emitter 1 when not combined with another emitter. λ2 is the maximum wavelength of emitter 2 when not combined with another emitter. λ1>λ2. Then, λ3, the maximum wavelength of the resulting emission (λ1>λ3>λ2) can be tuned by relative concentrations of the emitters 1 and 2. Devices were fabricated and spectra measured for a variety of different combinations of emitters. EL (electroluminescent) properties for the various emitters used in the experiments are shown in Table 2

TABLE 2 EL properties of the emitters used in the device examples 1931 CIE λ max FWHM Emitter x Y [nm] [nm] A 0.321 0.626 524 64 B 0.428 0.554 552 84 C 0.647 0.350 618 72 D 0.688 0.308 630 52

Example 1

FIG. 3 shows a schematic structure of devices that were fabricated having variable [%] of emitters C and D, used with Example 1.

Example 1 is based on devices having 2 emitters, C and D, deposited into the device EML in a variety of ratios, but with total concentration of the emitters constant C[%]+D [%]=7%. The devices EL is shown (FIG. 4) and the devices performance is summarized in Table 3:

TABLE 3 EL, JVL, LT performance of the devices Example 1 with variable [%] of emitters C and D At Example 1 At 1,000 nits At 40 mA/cm² CD 1931 CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) C % D % x y [nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 7 0.690 0.307 630 50 8.7 13 18.8 4.7 2 4,145 8 1 6 0.689 0.309 630 52 8.7 14 19.8 5.1 2 4,482 10 3 4 0.684 0.313 628 52 8 15.2 20.4 5.9 4 4,920 16 4 3 0.680 0.318 628 52 8.1 163 20.4 6.3 12 5,182 38 6 1 0.668 0.329 626 58 7.9 18.1 19.7 7.2 19 5,834 50 6.25 0.75 0.662 0.335 624 62 7.4 19 18.8 8.1 11 6,092 28 6.5 0.5 0.659 0.338 622 64 7.3 19.8 18.9 8.6 30 6,503 66 6.75 0.25 0.654 0.343 622 70 7.2 20.3 18.1 8.9 18 6,680 38 7 0 0.647 0.350 618 72 7.4 20.9 17 8.9 18 6,898 35 *Calculated assuming acceleration factor 1.8

FIG. 4 shows electroluminescent (EL) spectra of the devices of Example 1.

FIG. 5 shows maximum wavelength and full width half maximum (FWHM) values for the devices of Example 1. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 6 shows the FWHM difference (experimental vs. calculated) values for the devices of Example 1.

Example 1 (and the other examples) show the following:

The resulting experimental EL spectra of the devices measured in the examples is significantly narrower as compared to theoretically calculated superimposed EL spectra of individual emitters C and D (for Example 1, see FIGS. 5 and 6). A similar narrowing is also observed in Examples 3, 4, and 5, but not in Example 2. This narrowing is an unexpected result, which is opposite to results expected as described in many references (see below), where a broad emission spectra was obtained by placing 2 emitters in one emissive layer.

-   High-Brightness White Organic Light-Emitting Diodes Featuring a     Single Emission Layer. Chang, Mei-Ying; Wu, Chun-Chih; Lin,     Shih-Chin; Chen, Yi-Fan. Journal of the Electrochemical Society     (2009), 156(1), J1-J5. -   Broad wavelength modulating and design of organic white diode based     on lighting by using exciplex emission from mixed acceptors. Wang,     D.; Li, W. L.; Su, Z. S.; Li, T. L.; Chu, B.; Bi, D. F.; Chen, L.     L.; Su, W. M.; He, H. Applied Physics Letters (2006), 89(23),     23351111-233511/3. -   High-efficiency single dopant white electrophosphorescent     light-emitting diodes. Adamovich, Vadim; Brooks, Jason; Tamayo,     Arnold; Alexander, Alex M.; Djurovich, Peter I.; D'Andrade, Brian     W.; Adachi, Chihaya; Forrest, Stephen R.; Thompson, Mark E. New     Journal of Chemistry (2002), 26(9), 1171-1178. -   White emission from a single-component single-layer solution     processed OLED. Coya, Carmen; Ramos, Maria M.; Luna, Xenia; Alvarez,     Angel Luis; de Andres, Alicia; Blanco, Raul; Juarez, Rafael; Gomez,     Rafael; Segura, Jose Luis Proceedings of SPIE (2009), 7415(Organic     Light Emitting Materials and Devices XIII), 74151P/1-74151P/12. -   Efficient, color-stable fluorescent white organic light-emitting     diodes with single emission layer by vapor deposition from solvent     premixed deposition source. Jou, Jwo-Huei; Chiu, Yung-Sheng; Wang,     Chung-Pei; Wang, Ren-Yang; Hu, Huei-Ching. Applied Physics Letters     (2006), 88(19), 193501/1-193501/3. -   Efficient pure-white organic light-emitting diodes with a     solution-processed, binary-host employing single emission layer.     Jou, Jwo-Huei; Sun, Ming-Chen; Chou, Hung-Hsing; Li, Chien-Hung.     Applied Physics Letters (2006), 88(14), 141101/1-141101/3. -   White light emission from a single layer organic light emitting     diode fabricated by spincoating. Yang, J. P.; Jin, Y. D.;     Heremans, P. L.; Hoefnagels, R.; Dieltiens, P.; Blockhuys, F.;     Geise, H. J.; Van der Auweraer, M.; Borghs, G. Chemical Physics     Letters (2000), 325(1, 2, 3), 251-256.

Table 3 and FIGS. 4 and 5 illustrate that maximum wavelength, FWHM, and device CIE can be fine tuned in a predictable way within a range defined by individual emitters C and D by the changing of the relative % of emitters C and D in the device EML.

Examples 2, 3, 4 and 5 show results similar to those of Example 1, but for different combinations of emitters.

Example 2

FIG. 7 shows schematic structure for the devices of Example 2 with variable [%] of emitters A and B.

FIG. 8 shows EL spectra of the devices of Example 2 with variable [%] of emitters A and B.

FIG. 9 shows maximum wavelength and FWHM values for the devices in Example 2 with variable [%] of emitters A and B. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

Table 4 shows EL, JVL, and LT performance of the devices of Example 2 with variable [%] of emitters A and B.

TABLE 4 EL, JVL, LT performance of the devices Example 2, with variable [%] of emitters A and B At Example 2 At 1,000 nits At 40 mA/cm² AB 1931 CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) A % B % x y [nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 12 0.428 0.554 552 84 5.9 47.6 14.2 25.2 224 14,494 115 3 9 0.421 0.560 550 82 5.7 50.4 14.9 27.7 275 15,152 130 6 6 0.407 0.571 548 82 5.6 54.6 15.9 30.7 215 16,208 90 8 4 0.396 0.578 546 82 5.4 55.9 16.2 32.3 152 16,781 60 9 3 0.388 0.583 544 82 5.4 58.1 16.7 33.6 145 17,123 55 10 2 0.375 0.592 538 82 5.3 57.6 16.4 34.4 174 17,264 65 11 1 0.354 0.606 528 74 5.3 58.9 16.6 35.1 108 17,400 40 11.5 0.5 0.341 0.614 526 70 5.2 57.5 16.1 34.8 67 17,038 26 12 0 0.321 0.626 524 64 5.3 57.4 16 33.8 48 16,700 19 *Calculated assuming acceleration factor 1.8

Example 3

FIG. 10 shows a schematic structure for the devices in Example 3 with variable [%] of emitters B and C.

FIG. 11 shows EL spectra for the devices of Example 3 with variable [%] of emitters B and C.

FIG. 12 shows maximum wavelength and FWHM values for the devices of Example 3 with variable [%] of emitters B and C. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

Table 5 shows EL, JVL, and LT performance of the devices of Example 3 with variable [%] of emitters B and C.

TABLE 5 EL, JVL, LT performance of the devices Example 3 with variable [%] of emitters B and C At Example 3 At 1,000 nits At 40 mA/cm² BC 1931 CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) B % C % x y [nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 12 0.655 0.343 622 74 6.7 16.6 14.9 7.7 15 5,729 40 3 9 0.652 0.346 620 74 6.9 17.8 15.4 8.0 28 6,323 63 6 6 0.645 0.351 618 72 6.9 19.2 15.5 8.7 37 6,986 70 8 4 0.640 0.356 618 72 6.8 21.3 16.3 9.9 108 7,766 170 9 3 0.634 0.362 618 72 6.7 22.8 16.6 10.6 165 8,303 230 10 2 0.616 0.379 608 70 6.7 26.4 16.9 12.4 193 9,552 210 11 1 0.590 0.404 606 68 6.5 31.2 17.2 15.1 217 11,082 180 11.5 0.5 0.553 0.439 602 72 6.2 36.8 17.1 18.6 174 12,886 110 12 0 0.457 0.530 562 90 5.9 47.3 14.8 25.2 63 15,789 28 *Calculated assuming acceleration factor 1.8

Example 4

FIG. 13 shows a schematic structure for the devices of Example 4 with variable [%] of emitters A and D.

FIG. 14 shows EL spectra for the devices of Example 4 with variable [%] of emitters A and D.

FIG. 15 shows maximum wavelength and FWHM values for the devices of Example 4 with variable [%] of emitters A and D. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

Table 6 shows EL, JVL, and LT performance of the devices of Example 4 with variable [%] of emitters A and D.

TABLE 6 EL, JVL, LT performance of the devices Example 4 with variable [%] of emitters A and D At Example 4 At 1,000 nits At 40 mA/cm² AD 1931 CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) A % D % x y [nm] [nm] [V] [Cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 10 0.688 0.308 630 52 9.6 10.9 15.3 3.5 1 3372 8 3 9 0.691 0.307 630 54 7.8 11.8 17.1 4.7 3 3,885 15 6 6 0.687 0.310 630 50 7.7 13.3 18.8 5.4 6 4,503 26 8 4 0.681 0.315 630 50 7.3 14.6 19.6 6.3 11 5,057 36 9 3 0.674 0.321 628 48 7.3 15.9 20.1 6.8 18 5,492 52 10 2 0.657 0.336 626 48 6.9 18.2 20.6 8.3 19 6,353 42 11 1 0.614 0.375 626 44 6.6 23.1 20.7 11.0 17 7,850 26 11.5 0.5 0.548 0.434 622 44 6.1 29.9 19.8 15.4 10 10,020 10 12 0 0.356 0.604 528 76 5.4 54.4 15.2 31.8 20 16,738 8 *Calculated assuming acceleration factor 1.8

Example 5

FIG. 16 shows a schematic structure for the devices of Example 5 with variable [%] of emitters B and D.

FIG. 17 shows EL spectra for the devices of Example 5 with variable [%] of emitters B and D.

FIG. 18 shows maximum wavelength and FWHM values for the devices of Example 5 with variable [%] of emitters B and D. Both measured experimental data and results calculated by adding spectra proportional to emitter concentration are shown.

FIG. 19 shows chemical structures for compounds used in device fabrication

Table 7 shows EL, JVL, and LT performance of the devices of Example 5 with variable [%] of emitters B and D.

TABLE 7 EL, JVL, LT performance of the devices Example 5 with variable [%] of emitters B and D At Example 5 At 1,000 nits At 40 mA/cm² BD 1931 CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) B % D % x y [nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 10 0.688 0.308 630 52 9.6 10.9 15.3 3.5 1 3372 8 4 8 0.69 0.31 632 52 7.6 12.6 18.3 5.2 6 4,172 29 6 6 0.687 0.31 630 50 7.6 14 19.8 5.7 9 4,770 36 8 4 0.677 0.32 628 50 7.5 14.9 19.2 6.2 32 5,265 100 10 2 0.646 0.35 626 46 7.1 19.5 20 8.6 46 6,888 90 11 1 0.6 0.39 624 46 6.8 24.7 19 11.3 79 8,524 105 11.5 0.5 0.541 0.45 622 48 6.4 32.1 17.5 15.8 64 10,888 55 12 0 0.457 0.53 562 90 5.9 47.3 14.8 25.2 63 15,789 28 *Calculated assuming acceleration factor 1.8

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore includes variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

1. A first device, comprising: an anode; a cathode; an emissive layer disposed between the anode and the cathode, the emissive layer further comprising: a first organic emitting material having a first peak wavelength; a second organic emitting material having a second peak wavelength; wherein the emissive layer has a homogenous composition; wherein the second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.
 2. The first device of claim 1, wherein the first and second organic emitting materials are phosphorescent organic light emitting materials.
 3. The first device of claim 1, wherein the second peak wavelength is between 12 and 28 nm greater than the first peak wavelength.
 4. The first device of claim 1, wherein the FWHM of the emissive spectrum of the first device is less than the greater of the FWHM of the emissive spectrum of (i) a second device that is the same as the first device in all respects except that it includes the first emitting material but not the second emitting material, and (ii) a third device that is the same as the first device in all respects except that it includes the second emitting material but not the first emitting material.
 5. The first device of claim 1, wherein the first device emits a third peak wavelength that is between the first peak wavelength and the second peak wavelength.
 6. The first device of claim 1, wherein: the first device emits a third peak wavelength that is between the first peak wavelength and the second peak wavelength; the concentration of the first organic emitting material in the emissive layer is C1, the concentration of the second organic emitting material in the emissive layer is C2, the first, second and third peak wavelengths are λ1, λ2, and λ3, respectively, and the third peak wavelength λ3 is within 4% of: ((λ1C1)+(λ2C2))/(C1+C2).
 7. The first device of claim 1, wherein the measured FWHM of the emissive spectrum of the first device is less than the combined emission of the first and second emitting materials calculated based on the proportions of the first and second emitting materials present in the emissive layer.
 8. The first device of claim 1, wherein the measured FWHM of the emissive spectrum of the first device is at least 10% less than the combined emission of the first and second emitting materials calculated based on the proportions of the first and second emitting materials present in the emissive layer.
 9. The first device of claim 1, wherein the first device is an organic light emitting device.
 10. The first device of claim 1, wherein the first device is a panel comprising a plurality of organic light emitting devices controlled by an active matrix.
 11. The first device of claim 1, wherein the first device is a consumer product.
 12. A method of fabricating a first device, comprising: providing a first container that contains, in a desired proportion: a first organic emitting material having a first peak wavelength; a second organic emitting material having a second peak wavelength providing a substrate having a first electrode disposed thereon; depositing an emissive layer over the first electrode, wherein the first container is a source of material for depositing, and wherein the emissive layer comprises the first and second organic emitting materials in the desired proportion; depositing a second electrode over the first emissive layer, and wherein the second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.
 13. The method of claim 16, wherein depositing the emissive layer further comprises depositing an organic host along with the first and second organic emitting materials.
 14. The method of claim 16, wherein the organic host is provided in the first container along with the first and second organic emitting materials, and is deposited from the first container.
 15. The method of claim 18, wherein the organic host is deposited from a second container. 